A walking-beam conveyor comprises a pair of fixed and parallel side beams flanking a central movable beam that can be reciprocated both vertically and horizontally. A workpiece can rest on the fixed beams, but be lifted from them by the movable beam as it moves from a lower position below the fixed beams to an upper position above these fixed beams. When the workpiece is resting wholly on the movable beam in the raised position thereof, this movable beam can be stepped horizontally forwardly to displace the workpiece horizontally whereupon the movable beam drops back down below the fixed beams to redeposit the workpiece on the fixed beams. The movable beam can then move, while remaining in the lower position, back to its starting position for another lift-advance and drop-retract cycle. In this manner it is possible to move extremely heavy and bulky objects along a horizontal path with relative ease. Such a system is particularly useful in a steel mill or the like where the workpieces to be moved about are very heavy but not fragile. The instant invention is particularly aimed at a system for conveying coils of sheet metal from place to place.
Most such arrangements use separate drives for vertical and horizontal reciprocation of the movable beam. To this end short hydraulic lifters or rams are provided at intervals along the movable beam, and engage the underside of the movable beam via rollers that are spaced vertically between the lifters and the movable beam. Thus these lifters can raise and lower the rollers on which the movable beam is longitudinally displaceable. Furthermore a longitudinal-displacement motor is provided on a vertically displaceable head carried by the lifters and engages a rack on the underside of the movable beam for horizontally displacing it. It is also known to connect the movable beam by means of a link pivoted at both ends to a horizontally expansible cylinder mounted underneath the assembly and vertically nondisplaceable.
Such arrangements have the considerable disadvantage that it is necessary to make a relatively deep foundation underneath the conveyor, as such a walking-beam conveyor is normally mounted flush with the floor. It therefore becomes necessary to form a relatively deep trench with the foundation to house the relatively tall structure that serves to horizontally and vertically displace the movable beam. Even in systems such as described in my above-cited copending application Ser. No. 007,608 filed Jan. 29 1979 the overall height of the conveyor is relatively great. This is extremely disadvantageous when ground conditions do not permit such a deep foundation to be installed. In any case such a conveyor becomes very expensive to install.